U.S. Pat. No. 4,393,673 (Widen) describes a cylinder lock provided with a side bar and pin tumblers of the aforesaid kind, in which the bottom surfaces of the rotatable pin tumblers are intended to coact with a coded, shouldered side part of the key. The coded surfaces engage with a segment-shaped part of the bottoms of respective pin tumblers, and curved transition parts whose radii correspond to the radii of the pin tumblers are provided between the coded surfaces of the key.
The side bar is spring-biased outwardly from the cylinder, into engagement with a recess in the lock housing, this recess being configured to urge the side bar into the cylinder plug upon rotation thereof, after having inserted the correct key into an operative position in the plug. The side bar includes a number of lugs having rounded engagement surfaces which coact with waisted parts of the side bar. In manufacture, the coded surfaces and the intermediate transition surfaces must be produced very accurately, and consequently the cylinder lock taught by this prior publication is comparatively expensive in manufacture.
U.S. Pat. No. 3,264,852 (Gysin) teaches a cylinder lock with which there is used a key which is provided on the side surfaces thereof with grooves which, when the key is inserted to an operative position in the plug, coact with tumblers that have outwardly projecting pins which engage in respective grooves. The tumblers of this lock do not coact with a side bar. Moreover, the pins on the tumblers are subjected to a relatively high degree of wear, which is liable to jeopardize the function of the cylinder lock after long-time use.
Other examples of the state of the prior art with regard to lock keys are found in SE B 380,861 (Winkhaus) and AU B 371,883 (Prunbauer).